1. Field of Invention
The invention relates to a noise shaping circuit and, in particular, to a circuit and method for shaping noises, which are applied to an analog-to-digital converting circuit.
2. Related Art
In an analog-to-digital converting circuit, a feedback loop is often formed by an analog-to-digital converter (ADC). However, multi-bit analog-to-digital converter may cause a nonlinear effect due to element mismatch. Moreover, the circuit is equivalent to one adding a noise source to the signal input terminal of the analog-to-digital converting circuit if the imperfect linear transformation are not trimmed or the noises caused by that are not shaped. Therefore, the performance of the circuit is reduced. Herein, related techniques and research can be found in U.S. Pat. Nos. 6,642,873, 6,469,648, 6,304,608, 6,266,002, 6,366,228, and 6,218,977. Please also refer to R. Schreier and B. Zhang, “Noise-Shaped Multibit D/A Convertor Employing Unit Elements,” Electronics letters, Vol. 31, No. 20, P1712-P1713, 28th Sep. 1995; H. Lin, J. Barreiro da Silva, B. Zhang and R. Schreier, “Multi-Bit DAC with Noise-Shaped Element Mismatch,” Connecting the World, 1996 IEEE International Symposium, Vol. 1, P235-P238, May 1996; L. Richard Carley, “A Noise-Shaping Coder Topology for 15+ Bit Converters,” IEEE Journal of Solid-State Circuits, Vol. 24, No. 2, P267-P273, Apr. 1989; and R. T. Baird and T. S. Fiez, “Linearity Enhancement of Multibit ΔΣ A/D and D/A Converters Using Data Weighted Averaging,” IEEE Transactions on Circuits and Systems-II: Analog and Digital Signal Processing, Vol. 42, No. 12, P753-P762, Dec. 1995.